Intercomparison exercises as a tool for improving the quality of radiochemical measurements in drinking waters - Radon-222 determinations.

The results of a European intercomparison on 222Rn in water were analyzed to evaluate the performances of standard and non-standard methods. Then, results obtained with a specific LSC method (ISO 13164-4) based on two-phase liquid scintillation counting which has been employed by a considerable number of participants were examined in detail. This ISO LSC method was proved to be accurate, reliable and its reproducibility has been also sufficient. The intercomparison could be used as a collaborative study and the analysis of its results allowed to estimate the method reproducibility.

Alpha-particle emission probabilities of 231Pa derived from first semiconductor spectrometric measurements.

The nuclide 231Pa is a member of the 235U decay chain. It is a complex alpha emitter with 25 identified alpha emissions. Formerly published alpha-particle emission probabilities were derived from measurements taken with magnetic spectrometers. This work presents the first measurements made with semiconductor detectors. High-resolution alpha-particle spectrometry was carried out at CIEMAT and JRC using ion-implanted planar silicon detectors. Alpha-particle emission probabilities of 23 transitions were derived from deconvolutions of the spectra. For the major lines, uncertainties are lower than 1%, a significant improvement to existing data. The new data set will allow a more accurate evaluation of the decay scheme of 231Pa.

Radon and thoron parallel measurements in Hungary.

Hungarian detectors modified and developed at the National Institute of Radiological Sciences (NIRS), Japan were placed at different sites, including homes and underground workplaces in Hungary, in order to gain information on the average radon (222Rn) and thoron (220Rn) concentration levels. Measurements were carried out in dwellings in a village and a manganese mine in Hungary. The radon and thoron concentrations in the dwellings of the village in the summer period were found to be 154 (17-1083) and 98 (1-714) Bq m(-3), respectively. Considering the results of other radon measurements during the winter (814 Bq m(-3)) and summer (182 Bq m(-3)) periods, the thoron concentrations were also expected to be higher in winter. In the manganese mine, radon and thoron were measured at 20 points for 6 months, changing the detectors each month. The averages were 924 (308-1639) and 221 (61-510) Bq m(-3) for radon and thoron, respectively. These results showed significant variance with the date and place of the measurement.

Radiation dose from coal slag used as building material in the Transdanubian region of Hungary.

Coals mined in the Transdanubian region in Hungary have an elevated concentration of (226)Ra, which becomes enriched in the slag after burning. This slag has been used as filling and/or insulating material in building works. The aim of this study was to investigate the radiological situation in this territory in terms of the possible impact of this residual material from coal. Flats in three towns with a coal mine and a coal-fired power plant operating in their neighbourhood were examined. The radionuclide contents (including (226)Ra, (232)Th and (40)K) of the slag used for building were determined, and the slags were categorised according to the international standards and recommendations. The external gamma dose rate and the radon concentration in the sites were measured, and based on these data dose assessments were made. The (226)Ra concentration of the slag was 160-2,893 Bq kg(-1); the indoor gamma dose rates were 82-633 nGy h(-1); the radon concentration measured with a nuclear track detector varied from 29 to 1,310 Bq m(-3); the assessed dose contributions in the three towns were 0.65-1.57 mSv y(-1) due to gamma radiation and 2.2-15.2 mSv y(-1) due to radon.

Critical remarks on gross alpha/beta activity analysis in drinking waters: conclusions from a European interlaboratory comparison.

The most common gross alpha/beta standard methods used for drinking water analysis are discussed, and sources of interferences are reviewed from a metrological point of view. Our study reveals serious drawbacks of gross methods on the basis of an interlaboratory comparison analyzing commercial mineral water samples with the participation of 71 laboratories. A proposal is made to obtain comparable measurement results using true standardized methods.

Alpha-particle emission probabilities of ²³6U obtained by alpha spectrometry.

High-resolution alpha-particle spectrometry was performed with an ion-implanted silicon detector in vacuum on a homogeneously electrodeposited (236)U source. The source was measured at different solid angles subtended by the detector, varying between 0.8% and 2.4% of 4π sr, to assess the influence of coincidental detection of alpha-particles and conversion electrons on the measured alpha-particle emission probabilities. Additional measurements were performed using a bending magnet to eliminate conversion electrons, the results of which coincide with normal measurements extrapolated to an infinitely small solid angle. The measured alpha emission probabilities for the three main peaks - 74.20 (5)%, 25.68 (5)% and 0.123 (5)%, respectively - are consistent with literature data, but their precision has been improved by at least one order of magnitude in this work.

High-resolution alpha-particle spectrometry of ²³8U.

The alpha-particle emission probabilities associated with the three main alpha transitions of (238)U were measured by high-resolution alpha-particle spectrometry. Highly enriched (238)U material was used and its isotopic composition characterised by mass spectrometry. Source production through electrodeposition was optimised to reconcile conflicting demands for good spectral resolution and statistical precision. Measurements were performed at IRMM and CIEMAT for 1-2 years in three different set-ups. A new magnet system was put into use to largely eliminate true coincidence effects with low-energy conversion electrons. Finally the accuracy and precision of the relative emission probabilities for the three transitions - 77.01 (10)%, 22.92 (10)% and 0.068 (10)%, respectively - have been improved significantly.

Half-lives of 221Fr, 217At, 213Bi, 213Po and 209Pb from the 225Ac decay series.

The half-lives of (221)Fr, (217)At, (213)Bi, (213)Po, and (209)Pb were measured by means of an ion-implanted planar Si detector for alpha and beta particles emitted from weak (225)Ac sources or from recoil sources, which were placed in a quasi-2π counting geometry. Recoil sources were prepared by collecting atoms from an open (225)Ac source onto a glass substrate. The (221)Fr and (213)Bi half-lives were determined by following the alpha particle emission rate of recoil sources as a function of time. Similarly, the (209)Pb half-life was determined from the beta particle count rate. The shorter half-lives of (217)At and (213)Po were deduced from delayed coincidence measurements on weak (225)Ac sources using digital data acquisition in list mode. The resulting values: T1/2((221)Fr)=4.806 (6) min, T1/2((217)At)=32.8 (3)ms, T1/2((213)Bi)=45.62 (6)min, T1/2((213)Po)=3.708 (8) µs, and T1/2((209)Pb)=3.232 (5)h were in agreement only with the best literature data.

Decay data measurements on 213Bi using recoil atoms.

In this work, (213)Bi has been separated from an open (225)Ac source by collecting recoil atoms onto a glass plate in vacuum. The activity of such recoil sources has been measured as a function of time, using an ion-implanted planar Si detector in quasi-2π geometry. From these measurements, a new half-life value of T1/2((213)Bi)=45.62 (6)min was derived. Additionally, high-resolution alpha-spectrometry measurements were performed at a solid angle of 0.4% of 4πsr, to verify the energies and emission probabilities of the α-emissions from (213)Bi. Using (225)Ac, (221)Fr, (217)At and (213)Po peaks as reference peaks, the measured (213)Bi α-peak energies at Eα,0=5878 (4)keV and Eα,1=5560 (4)keV were about 10keV higher than validated data. The relative α-particle emission probabilities of (213)Bi, Pα,0=0.9155 (11) and Pα,1=0.0845 (11), and the (213)Bi alpha branching factor, Pα=1-Pß=2.140 (10)%, are compatible with recommended values, but have a higher accuracy.

Radiological investigation of the effects of red mud disaster.

On 4 October 2010, the gate of a red mud waste dump of a Hungarian alumina factory was damaged and ∼800.000 m(3) of alkaline red mud flooded the vicinity of the dumps. Red mud samples were collected from the contaminated area and they were investigated from the radiological point of view. The activity concentrations were as follows: (232)Th: 264 (194-337) Bq kg(-1), (238)U: 265 (197-332) Bq kg(-1), (226)Ra: 180 (143-237) Bq kg(-1), (40)K: 283 (228-360) Bq kg(-1). As a function of the moisture content (0-28 %), the obtained radon emanation coefficients were relatively high (7.6-20 %) and, consequently, the radon exhalation also increased.

Measurement of the 226Th and 222Ra half-lives.

The half-lives of (226)Th and (222)Ra were measured by counting alpha-particle emissions from sources as a function of time. The (226)Th sources were prepared from an open (230)U source, capturing recoil atoms after alpha-particle decay on glass disks or even directly onto a detector. Similarly, the (222)Ra sources were obtained by self-transfer of recoil atoms from (226)Th sources. The activity measurements were performed in (nearly-)2π geometry with an ion-implanted silicon detector. The decay curves were analysed in different ways, incl. moment analysis, trying to avoid the pitfalls of bias of least-squares fits to Poisson distributed data. The observed half-life values are T(1/2)((226)Th)=30.70 (3) min and T(1/2)((222)Ra)=33.6 (4) s. Literature values show some inconsistency.

Measurements of the half-life of 214Po and 218Rn using digital electronics.

The half-lives of (214)Po and (218)Rn have been measured. The radionuclides were produced in the decay of a (230)U source and the emitted alpha-particles were measured in nearly-2π geometry with an ion-implanted planar silicon detector. The data acquisition was performed with a digitiser operated in list mode, saving the energy and time of detection (10 ns precision timestamp) of each event. The half-lives were deduced from the time differences between the alpha-decays populating the nuclide of interest and those corresponding to its decay. Different methods were applied, based on delayed coincidence counting and time-interval distribution analysis. The resulting half-lives are 33.75 (15) ms for (218)Rn and 164.2 (6) µs for (214)Po, both in agreement with some of the literature values, and obtained with higher precision in this work.

High-resolution alpha-particle spectrometry of the 230U decay series.

High-resolution alpha-particle spectrometry was performed on the (230)U decay series. A (230)U source was prepared on a stainless steel disc by electrodeposition in an ammonium nitrate solution. Spectrometry of the alpha-particle energy spectrum was performed with ion-implanted planar silicon detectors in vacuum. A set of alpha emission probabilities is presented for (230)U and (226)Th. The measured peak intensities were corrected mathematically for coincidental detection of alpha-particles and conversion electrons emitted in the same decay. A good agreement with literature data was observed. The uncertainty budget and the correlation matrix are presented. The validity of the alpha-particle energies was tested and could be confirmed for most peaks within a few keV, but discrepancies were found for the 2nd peak of (226)Th and the main peak of (218)Rn.

Measurement of the 225Ac half-life.

The (225)Ac half-life was determined by measuring the activity of (225)Ac sources as a function of time, using various detection techniques: α-particle counting with a planar silicon detector at a defined small solid angle and in a nearly-2π geometry, 4πα+ß counting with a windowless CsI sandwich spectrometer and with a pressurised proportional counter, gamma-ray spectrometry with a HPGe detector and with a NaI(Tl) well detector. Depending on the technique, the decay was followed for 59-141 d, which is about 6-14 times the (225)Ac half-life. The six measurement results were in good mutual agreement and their mean value is T(1/2)((225)Ac)=9.920 (3)d. This half-life value is more precise and better documented than the currently recommended value of 10.0 d, based on two old measurements lacking uncertainty evaluations.

Measurement of the 230U half-life.

The (230)U half-life was determined by measuring the decay curve of (230)U sources by various nuclear detection techniques: α-particle counting at a defined small solid angle; 4πα+ß counting with a windowless CsI sandwich spectrometer, a liquid scintillation counter and a pressurised proportional counter; gamma-ray spectrometry with a HPGe detector and nearly-2π α-particle counting with an ion-implanted silicon detector. Depending on the technique, the decay was followed for 100-200 d, which is 5-10 times the (230)U half-life. The measurement results of the various techniques were in good mutual agreement. The mean value, T(1/2)((230)U)=20.23 (2) d, is lower than the literature value which is based on one measurement in 1948 and resulted in a half-life value of 20.8d without statement of uncertainty. A correction for the ingrowth of the long-lived (210)Pb and its daughter products may have been overlooked in the past.

Solid thoron source preparation in a porous mineral matrix.

Thoron and progeny are decay products of (232)Th with a great impact on human health. The release of thoron gas from the mining and milling of thorite, monazite and other major thorium ores has been recognised as a potential radiological health hazard. For precise measurements, calibration is a very important factor. This paper describes a cheap and easy way of producing a stable thoron source made of thorium nitrate packed in a porous clay mineral matrix used as (220)Rn generator. The source should have a small spherical shape and be fired at 600°C; this will lead to a great pore volume, necessary for the thoron gas. High importance should be given to the water uptake. The exhalation power of (220)Rn was measured using a Lucas scintillation cell. Experimental efficiency values obtained ranged between 0.16 and 1.44 %.

Dependence of radon emanation of red mud bauxite processing wastes on heat treatment.

Natural radioactivity content, radon emanation and some other physical characteristics of red mud were investigated, so that to identify the possibilities of the safe utilization of such material as a building material additive. Based on the radionuclide concentration, red mud is not permitted to be used directly as a building material, however, mixing of a maximum 20% red mud and 80% clay meets the requirements. The main aim of this work was to determine the dependence of the emanation factor of red mud firing temperature and some other parameters. The relevant experimental procedure was carried out in two different ways: without any additional material, and by adding a known amount of sawdust (5-35 wt%) then firing the sample at a given temperature (100-1000 degrees C). The average emanation factor of the untreated dry red mud was estimated to 20%, which decreased to about 5% at a certain heat treatment. Even lower values were found using semi-reductive atmosphere. It has been concluded that all emanation measurements results correlate well to the firing temperature, the specific surface and the pore volume.